Motorizing this trycicle

[Kaj] wanted to help out an aging family member by building them an electric tricycle during international Hack Day back on August 11th. He mixed in some reused parts with some new ones and ended up with bike that lets the rider troll other cyclists. Apparently when serious riders see an older man on a trike gaining on them they pedal like mad to make sure they don’t suffer the embarrassment of being passed. But there’s enough power and range to overtake the strongest of non-powered competitors.

Many of the parts came from a non-functional electric bike sold on Craig’s List. [Kaj] reports that the bike was trashed, but the motor system was mostly salvageable. He replace the batteries and charger and hooked up the motor to the rear axle. The initial install placed everything but the motor in the basket behind the rider. The weight and placement made the thing unstable when cornering. The solution was to house the batteries in a tool box and strap it below the basket. The lower center of gravity makes sure the trike is easy to handle, and now there’s still room in the basket for your groceries.

16 thoughts on “Motorizing this trycicle”

The first thing I noticed, before reading the article, was that the bike had a hub motor in the front wheel. I just don’t understand how the article was written and posted saying that it had a motor on the rear axle… It obviously is not the case. Makes me wonder if this is only one example of the authors on HaD just making up information.

He really loves messing with those cyclists, gives him a big grin every time he rolls back up the driveway. He even pretends to pedal while he passes them.

When the “Electric” magnet is left off the battery box, it’s pretty stealth from the back. The speed controller is mounted on the frame behind the seat post, but I left it uncovered to keep the heatsinks cool.

The ones I’ve seen don’t have true differential gearing. Instead, they only drive one of the two rear wheels and let the other one spin freely. Normally this is OK, but if you are riding in a very tight circle or if the drive wheel loses traction, it can be a problem.

Another interesting note: Tricycles are actually somewhat stable on two wheels. You can go around a hard corner to get it up on two wheels, then straighten out an continue to ride in a straight line on two wheels. It’s like riding a bike, but a bit more work to keep it balanced since the center of gravity is high.

My uncle did a conversion to a trike similar to this except he put a petrol engine where the basket goes. He had it running through a centrifugal clutch so you could still pedal if you wanted to. He gave it to his Dad who was dying of lung cancer at the time so he could get around quicker. Almost killed him but boy did he have some fun on it.

The motor is 500W (2/3 HP) – This particular frame is rated for fairly heavy loads and has been used a few similar hub motor projects without issue. The torque curve on this motor lends itself for speed rather than hill climbing, with a nice gentle acceleration. No significant frame flex has been observed.

Steering stem failures on hub motors are rare, but fork failure usually involve either a suspension fork or 750+ watt hubs. The most common type of failure is “spin out”, where the hub axle spins in the dropouts, damaging wiring and possibly splitting the dropout. I have fitted the motor with an anti-spinout bracket that would prevent this even if the axle were completely loose.

My hometown is in the bottom of a valley, and it’s ~98% flat here. The steepest part of the trip is my driveway, and inertia does most of the work there.